Basso spent the 2021 campaign with the High–A Lansing Lugnuts, registering a 4.71 ERA with 26 strikeouts across 7 appearances (4 starts).[5] He underwent Tommy John surgery in June 2021, causing him to miss the remainder of the season and the entirety of the 2022 season as a result.[6] Basso returned from injury in 2023, splitting the year between Lansing and the Double–A Midland RockHounds. In 20 appearances (17 starts) between the two affiliates, he accumulated a 2.42 ERA with 64 strikeouts across 63+1⁄3 innings pitched.[7]
On November 15, 2023, the Athletics added Basso to their 40-man roster to protect him from the Rule 5 draft.[8] He was optioned to the Triple–A Las Vegas Aviators to begin the 2024 season.[9] On May 14, 2024, Basso was promoted to the major leagues for the first time.[10] However, he did not appear for Oakland and was optioned down to Las Vegas the next day.[11] On May 31, Basso was recalled to the majors following an injury to Lucas Erceg.[12] He made his MLB debut later that day against the Atlanta Braves, pitching a scoreless inning in relief and recording his first career strikeout against Marcell Ozuna.[13] In 7 games (4 starts) during his rookie campaign, Basso compiled a 1-1 record and 4.03 ERA with 19 strikeouts across 22+1⁄3 innings pitched.
On March 5, 2025, it was announced that Basso would be shut down after suffering a shoulder strain during a spring training outing.[14] On April 7, he was transferred to the 60-day injured list.[15] Basso was activated from the IL on August 11.[16] He made 11 appearances for the team, posting a 1-1 record and 2.31 ERA with eight strikeouts across 11+2⁄3 innings pitched.
Basso was optioned to Triple-A Las Vegas to begin the 2026 season.[17]